Method for reliably lighting cells in a plasma display panel

ABSTRACT

A method for significantly increasing the reliability of entering information into a plasma display panel having information holding cells in a central area and border cells around the perimeter of the panel, including repetitively firing the border cells in simultaneous sequence, and applying a selective address signal (write pulse) to the selected information cells at the time the border cells are being discharged.

United States Patent [1 1 Trogdon METHOD 'FOR RELIABLY LIGHTING CELLS IN A PLASMA DISPLAY PANEL Inventor; Ray L. Trogdon, Urbana, 111.

University of Illinois Foundation, Champaign County, 111.

Filed: Apr. 26, 1972 Appl. No.: 247,819

Assignee:

US. Cl. 315/169 R, 315/168 Int. Cl. H0lj 17/30 Field of Search 315/169 R, 169 TV, 167,

References Cited UNITEDSTATES PATENTS 3,559,190 l/197l Bitzer et a]. 315/169 TV [111 3,854,072 [4 1 Dec. 10, 1974 Kupsky 3l3/378 R Primary ExaminerJohn K. Corbin Assistant ExaminerRichard A. Rosenberger Attorney, Agent, or FirmMerriam, Marshall, Shapiro & Klose [5 7 ABSTRACT A method for significantly increasing the reliability of entering information into a plasma display panel having information holding cells in a central area and border cells around the perimeter of the panel, including repetitively firing the border cells in simultaneous sequence, and applying a selective address signal (write pulse) to the selected information cells at the time the border cells are being discharged.

4 Claims, 3 Drawing Figures PATENTEU DEC I 0 I974 sum 2 or 2 T0 0 POWER SUPPLY METHOD FOR RELIABLY LIGHTING CELLS IN A PLASMA DISPLAY PANEL This invention relates to plasma panel systems and in particular to an improved method for reliably entering informationinto a plasma panel.

The plasma panel is a two dimensional array of light emitting gas discharge elements that exhibits inherent memory. This type of plasma panel has been previously described in U.S. Pat. No. 3,559,190 issued Jan. 26, 1971, on an applicatin of D. L. Bitzer, H. G. Slottow and R. H. Willson entitled Gaseous Display And Memory Apparatus", U. S Ser. No. 613,693, filed Dec. 22, I966, assigned to the same assignee as here. The plasma panel described in the aforementioned patent comprises a plurality of discharge cells having associated electrodes for discharging the gaseous medium within selected cells and forming corresponding cell wall charges, the presence or absence of wall charges conveying the desired information. The plasma panel is normally termed a plasma display panel although it is also useful as an information storage or memory panel, with or without its display capability.

Of common concern to those interested in successful operation of plasma display panels has been areliable process of changing cells from the off state, i.e., the state where no light is produced, to the on state which is the state where light is produced. It has been recognized that off cells are more easily turned on if they are located in close physical proximity to cells that are already on. Apparently thisis due to the requirements for the presence of some charged particles within the cell desired to be fired or discharged, as noted for example in the aforementionedpatent at column 10, lines 44-64. This phenomena has been exploited in practice by having lighted cells around the perimeter of a useful display area on the panel. For typical inputdata, e .g., a page of text, letters are first written near the perimeter of the'panel and the cells that comprise the first letter serve as pilot cells in providing somecharged particles for the second letter, etc.

In some systems, this phenomena has been exploited by writing a line of cells underneath the intended text. Usually the line is alternately extended and shortened so that it appears. only underneath the letter being formed. Another technique is to simultaneously write all cells in an array that defines the location of the intended letter and then to erase the unwantedcell locations. This technique is successful because the likelihood of writing one cell in the array is great and this cell can then serve as a starting cell for'writing the remainder of the array. Of course these approaches have disadvantages for unrestricted applications of displays.

Early efforts at dependable writing employed ultraviolet light sources external to the panel. However, glass severely attenuates the most effective light wavelengths so that this approach isinefficient and has largely been abandoned. v

In techniques which employed border cells around the panel the sustaining signals used for sustaining the addressable cells (information holding cells) are also used to drive or-discharge the border cells, and the border cells are thus fired at the same time as the sustaining discharges. While these techniques are satisfactory for turning on cells directly adjacent the border cells,

they are of limited value for turning on cells nearer to the center of even a small panel.

Indeed, the requirements of writing information into the panel discourage proper border cell utilization with most systems presently in use. This is due to the fact that signals with amplitudes less than the sustaining voltage, but large enoughwhen aided by wall charges to cause a discharge, have been found to tend to erase on cells. Accordingly, the selective addressing signals or write pulses must be in the same direction as the excursion of the preceding sustainer cycle. When this is done, the write signal is opposed rather than aided by the wall charges of on cells. Likewise, the wall charges of border cells are in a direction that prevents their being fired with the signals available.

Another problem in such simultaneous border/sustaining discharg'e systems arises from the fact that the border cells are located at the intersection of border electrodes and addressable electrodes. When writing information into the panel, the unselected addressable electrodes in these systems are normally treated to avoid undesirably firing associated cells.

Even more complicated, expensive and cumbersome techniques have been proposed (such as turning all of the off cells on and then back off with successive discharges while not disturbing the already on cells) to solvethis reliability of turn on problem, but none have been commercially successful. 7

SUMMARY OF THE INVENTION In accordance with the principles of the'present invention there is provided a method for significantly incells around the perimeter, a 10% probability of writing the innermost cells isobtained with the prior simultaneous border/sustaining discharge operation. Using the .method of the present invention the probability increased to almost v BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram illustrating various waveforms and their timing sequence in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating a plasma panel with X and Y border drive signal sources and'X and Y sustaining signal sources; and

FIG. 3 is a schematic diagram illustrating a typical circuit useful as either a sustaining signal source or border signal source.

DETAILED DESCRIPTION FIGS. l-3 illustrate. an embodiment useful in practicing the invention. As is shown in FIG. 2, a plasma display panel 10 includes-as is known in the art a series of corresponding X and Y, electrodes such that the intersection of any two electrodes can be selectively addressed by means of suitable addressing means coupled to the associated corresponding electrodes. The application of suitable addressing or drive signals forms a discharge of the gaseous medium within the respective cells thereby forming a corresponding cell wall charge. The formed wall charge opposes the drive signal thereby rapidly extinguishing the discharge. The presence or absence of wall charges convey the desired information. The information can be maintained in the panel by application of an alternating sustaining signal which by itself is not sufficient to discharge a cell without a wall charge, but is sufficient to discharge a cell having a wall charge on alternating half cycles of the sustaining signal.

The operation of selectively addressing the plasna display panel to write information, and the sustaining operation is well known in the art. Reference may be made to the aforementioned US. Pat. No. 3,559,190 for a specific description thereof.

For purposes of illustrating the present invention, in FIG. 2 there is shown X and Y sustaining signal sources, V,, which are coupled to the respective X and Y electrodes of display panel 10. Within the panel there isincorporated a number of cells around the perimeter or border of the panel as defined between the edges of panel 10 and the dashed line 12 indicated on FIG. 2 for convenience of illustration. It must be realized of course that these border cells can be and usually are identical to the information holding cells within the inner portion of the display panel 10 as bounded by the dashed line 12.

The border cells are associated .with the illustrated X border electrodes l4, l6 and 18, as well as the Y border electrodes 22, 24 and 26, 28. Such border cells are normally utilized only for the purpose of increasing the reliability of writing information into theinformation holding cells defined within dashed line 12.

. X and Y border signal sources, V are connected respectively tothe X border electrodes and the Y border electrodes as shown in FIG. 2. For purposes of illustration, a typical circuit which can be used for either the X and Y sustaining sources, V, or the border drivin signal sources, V,, is illustrated in FIG. 3'.

Referring to FIG/1, the various waveforms therein illustrated show the desired operation for reliably discharging or lighting cells in the plasma display panel 10 in accordance with the information. The first waveform is provided by the X sustaining-signal source to all of the X electrodes on the panel including electrodes 14 through 20. The second waveform 32 is provided by the Y border driving signal source toonly the Y electrodes 22, 24, 26, 28. The third waveform 34 represents the resulting differential voltage across the horizontal border cells, namely those which are associated with the respective electrodes 22, 24, 26, 28.

The next three waveforms 36, 38, can be similarly described as respectively associated with the Y sustaining signal source, the X border signal source, and the resulting differential voltage across the vertical border cells associated with the respective electrodes I4, l6, 18, 20.

. Following these waveforms, on FIG. 1 and 2 there is repeated the X and Y sustaining signals 30, 36. The resulting waveform'42 represents the differential voltage across cells in the information holding area of the panel asdefined within the dashed line 12. In the waveform 42, the small circles therein indicate the points where a sustaining voltage. has been applied to a cell having wall charges so as to cause a sustaining-discharge. In

particular, as in the prior art, the sustaining discharges occur during alternate half cycle portions of the waveform 42. Thus, for each of the points indicated by a small circle on waveform 42, the required sustaining signal voltage magnitude provided by a combination of signals 30 and 36 from the X and Y sustainers, respectively, is attained.

In operation, writing information into panel 10 is provided by well known addressing or write signals applied to corresponding electrodes associated with the selected information holding cell. Such selection is illustrated by a write pulse superimposed for convenience of illustration in FIG. 1 in association with waveform 42. As is known in the art, the write pulse is preferably positioned after a sustaining discharge and in the same direction as the last sustaining voltage excursion.

It has been found that the selectively addressed cells within the information holding area of panel 10 can be more reliably discharged or lighted by simultaneously discharging the border cells when information is being entered or written into the panel. Thus, as noted in FIG. 1, the X andY border cells are simultaneously repetitively discharged due to the combination of the respective sustainer signal and border drive signal. For instance as noted on waveform 34 the voltage resulting across the horizontal border cells associated with electrodes 22, 24, 26, 28 due to the combination of X sustainer signal 30 and Y border signal 32 is sufficient to repetitively discharge such border cells. The indicated small circles in FIG. 1 on resulting waveform 34 show such discharge points. Also, the X border driving signal 38 combines with the Y sustainer signal waveform 36 applied to-electrodes l4, l6, 18, 20, so as to discharge tion are understood to be given here only as examples.

Various apparatus and corresponding operating signals can be provided by those skilled in the art pursuant to the teachings herein in order to practice the invention. Therefore, various embodiments can be provided by those skilled in the art pursuant to these teachings in order to light or discharge the border cells simultaneously with the presence of a selective address or write signal.

In particular, it may be noted that FIGS. 1-3 illustrate the turning on of all four borders during the presence of a write signal. This is especially desirable for large panels. However, in the case of relatively small panels, the use of only one or two border areas can be found to enable reliable lighting of the information holding cells. In either event, the principle of the present invention of turning on the border cells during the time when a write pulse is present is utilized.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations shouldbe understood therefrom, as modifi'-' cations will be obvious to those skilled inthe art.

What is claimed is: I 1. In entering information into information cells in a plasma panel in response to an applied selective address firing signal,- sustaining signals being applied to said panel for sustaining the information entered into said panel. and said panel including a plurality of border cells around said information cells, an improved method for reliably entering said information comprising applying a border drive signal to said border cells for combining with said sustaining signals to discharge all of said plurality of border cells simultaneously with each application of said selective address firing signal.

2. In a plasma panel having information cells disposed in a substantially central area on said panel and a plurality of border cells disposed in horizontal and vertical border areas substantially surrounding said information cells, wherein information is entered into said panel by applying addressing signal to a selected cell and wherein said information entered into said panel is sustained in said panel by applying sustaining signals to said panel, an improved method for reliably entering said information comprising applying respective horizontal and vertical border drive signals to said.

border cells for combining with said sustaining signals to discharge all of said plurality of border c'ells comprising said horizontal and vertical border areas simultaneously with the application of said selective addressing signal to said selected cell.

3. The improved method of claim 2 wherein applying said sustaining signal comprises providing complementary X and Y sustaining signals;

said method further including,

applying said X sustaining signal and one of said horizontal and vertical border drive signals to respective border cells; and

applying said Y sustaining signal and the other of said horizontal and vertical border drive signals to the other of said respective border cells.

all of said plurality border cells thereby being discharged in repetitive simultaneous sequence.

4. ln entering information into a plasma display panel having a plurality of information cells disposed in a generally central area on said panel, a first pair of border cells on opposite sides of said panel on the perimeter of said information cells, a second pair of border cells on opposite sides of said panel on the perimeter of said information cells, wherein information is entered into said panel by applying a selective addressing signal and said entered information is sustained by applying a pair of sustaining signals, an improved method for reliably entering said information comprising:

providing a first border driving signal source supplying a first drive signal for said first pair of border cells;

providing a second border driving signal source supplying a second drive signal for said second pair of border cells;

applying one of said sustaining signals and said first drive signal to said first pair of border cells for repetitively discharging said first pair of border cells simultaneously;

applying the other of said sustaining signals and said second drive signal to said pair of border cells for repetitively discharging said second pair of border cells simultaneously with said repetitive discharges of said first pair of border cells; and

applying said selective addressing signal to said panel during the simultaneous discharging of said border cells. 

1. In entering information into information cells in a plasma panel in response to an applied selective address firing signal, sustaining signals being applied to said panel for sustaining the information entered into said panel, and said panel including a plurality of border cells around said information cells, an improved method for reliably entering said information comprising applying a border drive signal to said border cells for combining with said sustaining signals to discharge all of said plurality of border cells simultaneously with each application of said selective address firing signal.
 2. In a plasma panel having information cells disposed in a substantially central area on said panel and a plurality of border cells disposed in horizontal and vertical border areas substantially surrounding said information cells, wherein information is entered into said panel by applying addressing signal to a selected cell and wherein said information entered into said panel is sustained in said panel by applying sustaining signals to said panel, an improved method for reliably entering said information comprising applying respective horizontal and vertical border drive signals to said border cells for combining with said sustaining signals to discharge all of said plurality of border cells comprising said horizontal and vertical border areas simultaneously with the application of said selectIve addressing signal to said selected cell.
 3. The improved method of claim 2 wherein applying said sustaining signal comprises providing complementary X and Y sustaining signals; said method further including, applying said X sustaining signal and one of said horizontal and vertical border drive signals to respective border cells; and applying said Y sustaining signal and the other of said horizontal and vertical border drive signals to the other of said respective border cells, all of said plurality border cells thereby being discharged in repetitive simultaneous sequence.
 4. In entering information into a plasma display panel having a plurality of information cells disposed in a generally central area on said panel, a first pair of border cells on opposite sides of said panel on the perimeter of said information cells, a second pair of border cells on opposite sides of said panel on the perimeter of said information cells, wherein information is entered into said panel by applying a selective addressing signal and said entered information is sustained by applying a pair of sustaining signals, an improved method for reliably entering said information comprising: providing a first border driving signal source supplying a first drive signal for said first pair of border cells; providing a second border driving signal source supplying a second drive signal for said second pair of border cells; applying one of said sustaining signals and said first drive signal to said first pair of border cells for repetitively discharging said first pair of border cells simultaneously; applying the other of said sustaining signals and said second drive signal to said pair of border cells for repetitively discharging said second pair of border cells simultaneously with said repetitive discharges of said first pair of border cells; and applying said selective addressing signal to said panel during the simultaneous discharging of said border cells. 